1. Field of the Invention
The present invention relates to a false-twist textured yarn of a polyamide and a method and an apparatus for the production thereof. More particularly, the present invention relates to a false-twisted textured yarn of a polyamide having a high crimp development ability and being excellent in heat durability, and a method and apparatus for the production thereof.
2. Description of the Related Art
False-twist textured yarns of polyamides have been known from old, and they are superior to false-twist textured yarns of polyesters and other polymers in stretchability and they are widely used for the production of woven and knitted stretch fabrics. However, with increase of the grade of sportswear, requirements for stretch materials become severer and presently available false-twist textured yarns of polyamides hardly satisfy these requirements. In the field of clothes for which an especially high stretchability is required, a false-twist textured yarn of a polyamide is mix-woven or mix-knitted with a polyurethane yarn. This, however, results in increase of the manufacturing cost.
In one of methods for obtaining a high-stretch yarn without using a polyurethane yarn, two single yarns to which primary twists have been imparted are doubled, the doubled yarn is strongly twisted in the direction reverse to the direction of the initial twists, the twisted yarn is thermally set and the yarn is then detwisted so that the detwist number is substantially equal to the number of the final twists (see Japanese Examined Patent Publication (Kokoku) No. 33-6699).
A yarn having a high stretchability can be obtained according to this method. However, this method is defective in that the processing steps are complicated and the manufacturing cost becomes high.
There has been proposed another method in which a preoriented undrawn yarn (POY) is false-twisted with a large false-twist number (see Japanese Unexamined Patent Publication (Kokai) No. 50-42152). Though the manufacturing cost can be reduced in this method as compared with that in the former method, the stretchability of the obtained textured yarn is lower than that of the textured yarn obtained according to the former method, because high twists cannot be given to the POY.
For producing a false-twist textured yarn of polyamide at a high speed, there is widely adopted an in-draw texturing system in which a preoriented undrawn yarn (POY) is false-twisted simultaneously with drawing. In fact, when a friction type twister is utilized in this system, the processing speed is as high as 600 to 1000 m/min. On the other hand, the spinning speed of POY is going to reach a level of 3000 to 4000 m/min. However, the recent needs for higher productivity require further increase of both the false-twist texturing speed and the spinning speed of POY. Various problems should be solved before attaining this object. One of these problems is how to avoid occurrence of fluffs in a false-twisted textured yarn with increase of the false-twist texturing speed. This disadvantage becomes particularly serious when POY spun at a high spinning speed is utilized. The reason is presumed to be that the elongation of POY is reduced with increase of the spinning speed thereof. Moreover, if the titre of the yarn is increased, generation of fluffs becomes conspicuous. The reason is that if the titre is increased, the difference of the yarn length between the inner and outer layers of the yarn is increased and therefore, the outer layer of the yarn is strongly elongated and finally broken to readily cause fluffs.
The length of the yarn path in a false-twist texturing machine tends to be increased with the increase of the texturing speed and now reaches 4 to 5 m or more. Because of the limitation of the ceiling height in a mill, it is difficult to form such a long yarn path linearly in the vertical direction. Accordingly, as shown in FIG. 3, a false-twist texturing machine in which a primary heater 2 and a cooling device 3 are obliquely arranged is often adopted at the present. In view of the facility of the threading operation, it is preferred that a first feed roller 1 and a twister 4 be arranged within reach of the operator's hands. Therefore, a considerable distance more than 50 cm is produced between the first feed roller 1 and the entrance of the primary heater 2 and ballooning of the yarn tends to occur at that area. To prevent occurrence of ballooning of the yarn, a rotary type twist stopping member called "vane tensor" as shown in FIG. 4 is disposed in the vicinity of the entrance of the primary heater 2. However, this rotary member tends to increase formation of fluffs in the resultant false-twist textured yarn.
As pointed out hereinbefore, formation of fluffs in a false-twist textured yarn is aggravated by any of the following false-twist texturing conditions:
(1) High speed processing.
(2) Usage of POY spun at a high spinning speed.
(3) Usage of a yarn of a large titre.
(4) Usage of a false-twist texturing machine in which the distance between the first feed roller and the entrance of the primary heater is large.
Namely, according to any of the conventional techniques, it is difficult to perform the false-twist texturing operation of POY and obtain a desired textured yarn having a titre of more than 30 denier at a processing speed of at least 600 m/min and a draw ratio lower than 1.35 by using a false-twist texturing machine in which the distance between the first feed roller and the entrance of the primary heater is 50 cm or more.
There has been proposed a method in which instead of the above-mentioned rotary twist stopping member, yarn guide elements for forming a bending yarn path are disposed between the primary heater and the first feed roller to reduce the twist ascent to the first feed roller (see Japanese Examined Patent Publication (Kokoku) No. 53-7976). According to this method, formation of fluffs and reduction of strength are prevented (such the drawbacks are thought to be caused by partial drawing of the yarn and deformation of the yarn section at the nip point of the first feed roller), but the capacity of inhibiting the twist ascent is poor and this method is not suitable for attaining the object of the present invention. It is considered that, to enhance the capacity of inhibiting the twist ascent by this method, the number of yarn guide elements must be increased for further bending of the yarn path. However, this causes an increase of the resistance to running yarn as well as difficulty of the smooth threading.
There has been proposed still another method in which a satin-plated bar guide for bending the yarn path between the heater and the feed roller is disposed in the non-rotary state 200 to 450 mm before the ordinary yarn path and the yarn is half wrapped on this bar guide and turned back (see Japanese Examined Patent Publication (Kokoku) No. 58-48649). According to this method, the distance of the yarn path between the feed roller and the heater is prolonged by turning-back of the yarn, whereby uneven distribution of twists is prevented, causing the decrease of fluffs in the resultant yarn. However, this bar guide has no function of stopping twist ascent and of preventing occurrence of yarn ballooning. Furthermore, in this known method, the yarn tends to be flattened just at the beginning of false-twist texturing and to adhere to the guide. Especially in case of POY, yarn breakage is caused at that time.
A still further method has been proposed in Japanese Unexamined Patent Publication (Kokai) No. 50-42152, for preventing formation of fluffs in the draw-texturing process, in which double twisted portions of at least 3 per cm of yarn length are forcibly formed in a yarn being passing through the twisting zone of the process. This method is effective only when the false-twist texturing speed is as low as about 100 to about 200 m/min , but, at such a high speed as 600 m/min or more, the texturing operation becomes unstable and the yarn breakage is increased.